Leica Absolute Tracker monitors cutting of wind turbine tripods

HGG - The Netherlands

On behalf of a customer, Dutch company HGG developed a new type of bevel cutting system which has an integrated Leica Absolute Tracker with Absolute Interferometer. The tracker continuously monitors the cutting process. Using the measured data, the machine cuts 60 m long, 400 t tubes into individual sections – to accuracies of a fraction of a millimetre.

Many 3D cutting jobs worldwide are done through HGG machinery. Founded in 1984, HGG is the world’s only company fully devoted to steel profile cutting providing both tailor made machinery and knowledge to the highest standards. The machines are sold worldwide to leading companies in the offshore, steel construction, process piping, shipbuilding and other industries. HGG profiling machines provide quality cutting according to latest norms (ISO 9013), easy operating & programming and industry specific customization. They are built to last.

HGG manufactures bevel cutting machines that are particularly suitable for processing large components. “We like challenges,” says Peter Tool, R&D manager at HGG. “Our greatest strength is that we design our systems and software from the bottom up – so we retain flexibility. Short channels of communication allow us to come up with completely new processes in very little time,” adds Tool.

Measuring technique: The key to success
German manufacturer of wind turbine components EEW placed an order with HGG. EEW wished to manufacture foundation structures, known as tripods, for an offshore wind farm using high quality steel. The task was to produce cylindrical members cut precisely in 3D from 400 t, 60 m long, 6 m high steel tubes. HGG realised from this basic information that adopting the correct measuring technique would be key to the success of the project.

A tube weighing 400 t deforms under its own weight when placed on the cutting machine. This deformation changes the diameter of a tube by up to 20 mm and leads to undesirable drifts. However, the changes in diameter are not constant; when the tube rotates on the cutting machine – the ovality changes with the movement of the tube. In addition, a 60 m long tube sags several centimetres at mid-span between supports. The structural frame of the cutting machine itself also deforms while supporting this extremely heavy load. In the face of deformations like these, even the most accurate machines are incapable of delivering a clean cut. “A tube costs 100,000 €,” explains Peter Tool. “With expensive material like that, cutting errors cannot be allowed to happen.” Therefore Tool and his team decided to integrate a measuring system into the cutting machine.

No expensive scrap
The key idea: The user should know the position of the tube relative to the cutting machine at all times. If the exact coordinates and deformation of the tube on the machine are always known, it is possible to continuously compensate for the movement of the cutting head. Expensive scrap is eliminated.

Peter Tool quickly found a suitable method of control. He had become aware of the potential of laser trackers at an earlier trade fair and recognised that there was no alternative to the range capability of laser metrology for the dimensions of the parts in the EEW project. HGG decided to couple the Leica Absolute Tracker to the cutting machine: Only this system could ensure the necessary accuracy and adequate measuring range for the 60 m long tubes – the typical measurement volume of the Leica Absolute Tracker can even extend to 160 m. No other laser tracker could offer the desired accuracy over the large distances resulting from the requirement to position the measuring instrument in front of the tube.

Laser tracker monitors cutting head and component
“From the start we had one objective: The machine had to be capable of being operated precisely by a single person,” says Peter Tool. Therefore HGG fully integrated the Leica Absolute Tracker into the cutting machine – the operator does not have to know how to use the laser tracker. The instrument tracks several reflectors on the cutting head and on the tube. Every section of the tube is fitted with a reflector – which lets the cutting machine operator know how much the tube bends. The laser tracker supplies the coordinates of one point every 100 milliseconds. The cutting machine software also controls the tracker – a task made possible by the emScon programming interface developed by Leica Geosystems.

HGG installed the new cutting machine in the EEW production facility in Rostock, Northern Germany. Mounted on a 8 m high platform, the Leica Absolute Tracker monitors the movement of the cutting machine and the supported tube. The measuring system has to work in a very difficult environment. Components of these extreme dimensions and weights frequently give rise to vibrations. Peter Tool: “The racker dealt with these issues without any problem. The dust created from the cutting operations did not adversely affect the measurements. Even with several millimetres of dust in the reflectors, they always continued to work perfectly.”

Leica Absolute Tracker: Perfect for wind farm infrastructure dimensions
HGG supplied a metrology-aided cutting system capable of precisely cutting 60 m long tubes to an accuracy of 0.5 mm. Peter Tool is proud of this development: “Thanks to the Leica Absolute Tracker, the HGG machine is capable of cutting extremely large components such as those now in common use by wind turbine manufacturers. A task which our customer successfully performed with precision and reliability.”